How Does Evolution Occur? - Downtown Magnets High School
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Transcript How Does Evolution Occur? - Downtown Magnets High School
More on Natural Selection
Bio Standard 8a, 7a, b, and c
• Orgs differ by DNA they
possess.
• DNA: code that forms your
traits.
• DNA makes up genes- set of
instructions for one trait.
• Chromosomes carry the
genes.
• Some traits are dominant
(shows up in offspring) or
recessive (doesn’t show).
DNA
Chromosomes
Genotype and Phenotype
• Genotype: genes/DNA
that an org contains for
a trait.
• Phenotype:
observable/physical
traits of an individual.
• Natural selection works
on phenotypes, what
org looks like.
• States that individs whose
characteristics are well-suited
to the environment will
survive.
• Survival of the Fittest.
To Work…
Populations
have:
1) Variation
among
individuals
2) Pop. size had to increase
3) Traits Are Passed on to
Offspring
To Work..4) Struggle for
Survival
Peppered Moth Story:
Natural Selection Example
• England: 2 types of moths
(same species): black and
white.
• White: abundant, black: rare.
Peppered Moth Story:
Natural Selection Example
• Trees the moths
lived on were
whitish colored.
• Predatory birds
could only see
dark moths to eat.
Huge white
moth pops.
Then, the Industrial
Revolution happened…
Coal was burned…created
soot…
Trees
lined
with
soot…
SO…Now
who is best
fit for this
environment
??
• Black moths now camouflaged w/
trees.
• Black moths abundant, passed
on genes to offspring.
•Survival of the fittest!
•Natural selection works on an
individual’s phenotype (physical
features), not its genotype (DNA)
Types of Natural Selection
1) Stabilizing
Selection:
Selective
pressures select
against the 2
extremes of a trait.
• Ex: it is better to be
average!
Types of Natural Selection
2) Directional
selection: one
extreme of the
trait experiences
selection against
it.
• Ex: giraffes w/
short necks
Types of Natural Selection
3) Disruptive selection:
Selection pressures
act against individuals
in the middle of the 2
extremes of the trait.
• Ex: it’s not good to be
average
Peppered Moth Virtual Lab